Small internal combustion driven implements, such as power saws, are becoming quite popular and are produced in great volumes. One of the primary features which affects consumer acceptance of such product is its ability to start repeatedly and operate effectively over wide variations in speed. Thus, the ignition system for the internal combustion engine which is used for these devices must be durable, effective in operation over a wide range of speed and uniform in operation over a number of years. In the past, the ignition system for a single cylinder internal combustion engine of the type used for small power implements has been patterned after the normal ignition system of a motor vehicle. In that instance, a cam operated switch, known as points, was used to break the ignition coil primary winding to induce a sparking current at the output of the ignition coil secondary winding. Such points caused variations in the timing of the spark with respect to the movement of the piston within the cylinder. Also, such contacts or points are spark eroded and the operating block for the points wears extensively to require periodic maintenance and replacement.
In small engines of the type contemplated in the preferred embodiment of one aspect of the invention, the sparking current is created by a magneto which involves a rotating flywheel having permanent magnets with an outwardly extending flux field that moves in an annular path as the flywheel is rotated by the crankshaft of the engine. This rotating flux field induces a voltage in the primary of the ignition coil which creates a current that changes rapidly upon operation of the points to induce a high voltage in the secondary windings for use in sparking the spaced electrodes of the spark plug. One aspect of the present invention relates to an ignition system which is usable with an internal combustion engine having a magneto for creating the sparking voltage. A system in accordance with this aspect of the present invention removes the need for mechanical switching and provides a solid state ignition system for a magneto operated sparking arrangement for an internal combustion engine. In accordance with the preferred embodiment of this aspect of the invention, a cartridge can be used with a standard magneto ignition system to convert the system from mechanical switching to solid state operation.
Although solid state ignition systems have been used in certain internal combustion engines, such systems have not been developed commercially for use on magneto operated ignition systems. Also, solid state ignition systems often require complex expensive components for producing sparking voltages.